By Marina Burka, Courtesy of Penn State News
Humans are not conditioned to think about sound as a tangible, measurable entity. For the majority of us, it simply becomes part of the background, secondary to our more informative visual environment. But for Jenny Tennessen, a doctoral candidate in ecology, sound is the basis for her graduate research in the field of bioacoustics and is something that has always intrigued her.
“I’ve always played instruments,” she said. “I started piano when I was 3 years old, and I played French horn from elementary school until college. So the importance of sound to humans and nonhuman animals has always interested me.”
Then, for an assignment in a freshman class at the University of Wisconsin, Tennessen was given the opportunity to research and analyze anything she wanted.
“I chose to look at the relationship between sonar testing and whale strandings,” Tennessen recalled.
Those interests were always in the back of Tennessen’s mind; after completing her undergraduate degree in biology in 2005 and master’s degree in conservation biology in 2009, both from the University of Wisconsin, Tennessen entered the field of bioacoustics as a doctoral candidate at Penn State.
“If you’re truly passionate about something, you can make it happen.”
– Jenny Tennessen, a doctoral candidate
A cross-disciplinary science that combines biology with sound production, dispersion and perception in animals and humans, bioacoustics is a relatively new field.
“Part of that is due to advances in technology that have enabled such rapid growth in the last 20 years,” said Tennessen. She pointed to the cellphone sitting on the table and said, “There’s a voice recorder right in there. Without the rapid acceleration of technology in the last few decades, we wouldn’t be able to conduct the kind of research that is necessary for this field.”
For her graduate research, Tennessen is examining how novel acoustic environments affect ecological processes and interactions among organisms. Natural environments throughout the world are experiencing increasing levels of unnatural noise. Many animals rely on sound to communicate and unnatural noise may interfere with communication, which could have negative consequences on survival and reproduction. Studies of ecological impacts of increased noise on animals typically focus on noise from human activities, such as from transportation, but unnatural noise may also come from invasive species.
Tennessen’s research took her into southern Florida where she explored the effects of the invasive Cuban tree frog species on local tree frog populations. She recorded the calls of the Cuban tree frog, described as a “grating, raspy, snarling squawk,” and used the recordings in a playback experiment to determine if they elicited changes in the acoustic behavior of native green tree frogs, which have a similar call, and pine woods tree frogs, which have a markedly different call.
“We predicted that Cuban tree frog choruses would interfere with native species whose acoustic behaviors were similar,” she said, “and that these would be the most likely candidates to modify their acoustic behavior to avoid interference.”
Tennessen and her colleagues found that the green tree frog nearly doubled its call rate while the pine woods tree frog, which calls at a faster rate and a higher frequency, did not alter its acoustic behavior at all, supporting their original hypothesis.
“We don’t think of noise from an invasive species as being destructive, but these alterations by native tree frogs in which they’re calling at a faster rate not only requires them to use more energy, but also alerts predators to their location. Overall, it could be detrimental to their population’s survival.”
“Jenny’s research investigates an under-considered mode of impact of invasive species – that of competition for acoustic space,” co-adviser and assistant professor of biology Tracy Langkilde told the Animal Behavior Society in The Conservation Behaviorist. “She has identified an important and poorly understood area of research – that of the behavioral consequences of noise – and has developed elegant and creative ways of testing this important issue.”
In 2012, Tennessen received the Edward O. Wilson Conservation Award from the Animal Behavior Society (ABS) to support this research. The award is named for E.O. Wilson, one of the world’s most eminent scientists and pioneers in biodiversity conservation. She also received a dissertation research grant from the National Science Foundation.
She presented her results at the 21st International Congress on Acoustics (ICA 2013) this past May and was featured in a ScienceDaily article “Croaking Chorus of Cuban Frogs Make Noisy New Neighbors.”
In another project, Tennessen is investigating how shipping noise affects the communication range between mother and calf pairs of the endangered North Atlantic right whale in the Bay of Fundy, a key summer feeding ground. For the past two years, she and a team from Syracuse University, the New England Aquarium and the National Oceanic and Atmospheric Administration (NOAA), led by co-adviser Susan Parks (assistant professor of biology at Syracuse University), have been recording the communication between mothers and calves during separation just prior to weaning. She will be presenting her findings at the 20th Biennial Conference on the Biology of Marine Animals in Dunedin, New Zealand, this December.
When asked whether it can be discouraging to realize how significant human acoustic activity is on ecosystems, Tennessen responded, “People don’t like to deliberately impact wildlife. Instead, the problem is that we often don’t know how our actions affect entire ecosystems. So if I or other people can show conclusively that certain actions are having negative effects, then I think positive changes can come out of that.”
After completing her doctorate, Tennessen plans to continue research and hopefully teach at the university level. As parting advice, she urged, “If you’re truly passionate about something, you can make it happen. I grew up in the Midwest, and somehow went on to study whales and tree frogs – that’s not something that was within the boundaries of my Chicago suburb. So make it happen, because I think that ultimately, you’re most effective when doing something you love.”